Drafting instrument



Oct. l5, 1929.

o. A: TURNER DRAFTING INSTRUMENT Filed March 5. 1928` Patented Oct. 15, 1929 PATENT OFFICE OSCAR A. TURNER, OF CHICAGO, ILLINOIS DRAFTIN G INSTRUMENT Application led March 5, 1928. Serial No. 259,022.

My invention relates to drafting instru ments, and has for vits object the production of an instrument which co-operates with a plane surface and suitable pivots to prodiue curves which serve lto solve mathematical problems, and other curves useful in the production of-ornamental figures.

In the accompanying drawings F ig. 1 shows the instrument in the form ot'a carpenters square, and provided with graduations andv tracing points by which a variety of curves may be drawn;

F ig. 2 shows a diagram produced by the instrument, which diagram serves for the geometrical trisection of an angle by plane geometry; and y Fig. 3 shows the main part of the device in the formof a draftsmans triangle provided with graduations on two legs, and also provided with a plurality' of tracing points, some at least of which points have definite relationships to the graduations. p

In Fig. 1; the body 10 has an interior right angle at 11 and an exterior right angle at 12.

The legs 13 and 14n1ay be of any length.

Along the inside of leg 18 are gradita-tions marked 1, 2, 3, etc., and similar graduations may or may not be along the leg 14.

The graduations begin at the corner 11, but

may be along the outer edge, and may begin at any desired point. y

In the leg 14, and in a line which is an extension of the inner edge of leg 13, are small holes 15, 16, and 17. In leg 13, and in line with the inner edge of leg 14, are other holes 18 and 19. The distance ot' the hole 19 from -the corner 11 is the same as the distance of the graduation marked l from the same corner. In other words, the hole 19 is a unit distance from corner 11, and in a direction perpendicular to the line of the inner edge of leg 13.

Exactness for this particular point is given because it, in conjunction with two pivoting points which are twice the unit distance from each other, and the inner edges of the legs 13 and 14, serves toAtrace a curve whichI call a trilocus, which curve is part of a general diagram which I call a trisectroid An illustration of the operation of the apparatus by the curve drawn from this point will serve to show how said apparatus is used for various purposes. I have chosen this particular point for illustration because the triseetroid serves for a simple solution ot' the trisection of an angle.

Referring to Fi g. 2, from the center O, and with unity (the distance from 11 to 19) as a radius, draw the semi-circle ADB. At the extremities of the diameter AB, stick pins which Will form pivots. These pins may be common pins ordinarily sold in stores, and are here assumed to be ywithout sensible diameter. Then apply the body 10 to these pivots as shown in dotted lines.

If the body 10 is moved rotatively with its lower face against the surface on which the circle is drawn, and its interior edges are kept in contact with the pins A and B, then the point 11 will trace out: the semi-circle ADB. This is because of the fact that the angle 11 is a right angle, and the-fact that any angle, as ADB, inscribed Within a semi-circumference is a right angle. If a marker, as a pencil point, be inserted thru the hole 19 at the time the body 10 is moved as described, then the marker will trace the curve 19CE, which is the trilocus.

From O as a center, draw the line OC so that the angle BOO is the angle to be trisected. From the point where the line OO cuts the trilocus, draw the line AC, then the angle ACO Will be one-third of the angle BOO.

To prove this, from the point D, Where the line AC cuts the\circle, draw the line'DO, which isa vradius of the circle. But the line DO is equal to a radius by construction, as it .is the 'distance of the point 19 from the angle that is, each one is equal to .22%v The exterior angle DOB is equal to the sum of the interior angles at A and D, that is, it is equal to 4B.

But as the angle DOC equals 1", COB must equal 3a. y

The instrument shown in Fig. 3 has grad`1 nations in inches along one leg and graduations in the metric scale along the other'leg. The instrument is shown as a draftsmans triangle with various tracing points. It may, however, be made in other forms. The essentials are that it must be movable with respect to two pivots, and a fixed point in the instrument must travel in the arc of a circle while being so moved. Also, that there must be some other point on the instrument which may be used to trace another curve which will have a definite relationship to the arc traced.

I have used the term rays to designate those lines which go outward from the ends of the diameter A-B and cut the curve CE. Itis to be noted that the part of 'a r'ay between the circle and the curve is a fixed quantity for any particular curve', In Fig. 2, this distance is the radius ofthe circle. If the 'tracing had been thru any one of the holes 15, 16, 17 or 18, the dist-ance between the circle and the curve would have been the distance of the hole from the corner 11. v 1

What I claim is:

In a device of the classidescribed, a body having straight ed es furnishing an interior right angle, said ody having graduations along one edge beginning at the apex of said angle, and said body having a small .hole adapted to receive a tracing point, said hole being located in a line which is an extension of the straight edge of the other leg and at a distance from said apex which is a multiple of the distance of the first graduation from said apex.

l OSCAR A. TURNER7 

